Mac App Store codesignature checked by Lion or do we have to do it?

Question

There is lots of code around for receipt validation (e.g.: NPReceiptVerification) for the Mac App Store. But should I not also check that the code signature is correct?

Does Lion check the code signature on launch and refuse to launch? I don't see a reason why not, if there is one there. It looks like it does not check the signature from my simple test.

If someone changes the Info.plist will code sign verification fail? - OK answered that one myself: "Various components of the application bundle (such as the Info.plist file, if there is one) are also signed" from "About Code Signing" at Apple developer.